The Secretary, through the Service, shall provide for the operation of child-care centers at Department facilities in accordance with this section. The operation of such centers shall be carried out to the extent that the Secretary determines, based on the demand for the care involved, that such operation is in the best interest of the Department and that is practicable to do so. The centers shall be available for the children of Department employees and, to the extent space is available, the children of other employees of the Federal Government and the children of employees of affiliated schools and corporations created under
section 7361 of this title.